Dryers that adjust power based on non-linear profiles

FIELD OF THE INVENTION

The invention relates to the field of printing systems, and in particular, to dryer units for printing systems.

BACKGROUND

In continuous-forms printing systems, one or more marking engines are used to apply marking material (e.g., aqueous ink) onto a web of print media. The web is driven through the marking engines and into a dryer. The dryer proceeds to heat the web and dry the marking material onto the web. The web moves quickly across the printing system in order to enable fast printing speeds. For example, the web may travel at many linear feet per second through the printing system. This means that dryers must either occupy a large space within the print shop or use a great deal of heat to dry the web. For example, in many dryers, inked portions of the web transit the entire length of the dryer in a fraction of a second.

In dryers that apply a great deal of heat over a short period of time, it remains a problem to ensure that the web is properly dried. Too much heat can cause charring at the web, which may break the web and halt printing operations. At the same time, too little heat can result in marking material on the web remaining wet, resulting in smearing or transfer of marking material that in turn reduces print quality.

Thus, printing system operators continue to desire dryers with enhanced functionality and reliability.

SUMMARY

Embodiments described herein control dryers for printing systems. These dryers use non-linear power profiles that specify an amount of power to apply to a heating element of the dryer based on the speed of a web of print media traveling through the dryer. These dryers may also select a power profile based on the type of media of the web. In some embodiments, the dryers may further deviate from the non-linear power profiles in response to determining that portions of the web exiting the dryer are too dry or too damp. This allows a dryer to adjust power based on the speed of the web, yet also allows the dryer to compensate for variations in ambient temperature, humidity, etc. at the print shop.

One embodiment is a system for controlling a dryer. The system comprises a controller. The controller is operable to determine a speed of a web of print media traveling through a dryer, and to apply power to a heating element of the dryer based on a power profile that models a non-linear relationship between power applied to the heating element and speed of the web. The controller includes separate power profiles for different types of media, and the controller is further operable to determine a type of media for the web, and to select the power profile based on the type of media.

Another embodiment is a method for controlling a dryer. The method comprises determining a speed of a web of print media traveling through a dryer, and determining a type of media for the web. The method further comprises selecting a power profile based on the type of media, and applying power to a heating element of the dryer based on the power profile, where the power profile models a non-linear relationship between power applied to the heating element and speed of the web.

Another embodiment is a non-transitory computer readable medium embodying programmed instructions which, when executed by a processor, are operable for performing a method. The method comprises determining a speed of a web of print media traveling through a dryer, and determining a type of media for the web. The method further comprises selecting a power profile based on the type of media, and applying power to a heating element of the dryer based on the power profile, where the power profile models a non-linear relationship between power applied to the heating element and speed of the web.

Other exemplary embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below.

DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings.

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a drying system in an exemplary embodiment.

<figref idref="DRAWINGS">FIG. 2</figref> is a flowchart illustrating a method for drying a web of print media in an exemplary embodiment.

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram illustrating various power profiles for dryer systems in an exemplary embodiment.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating modifications applied to a power profile for a dryer system in an exemplary embodiment.

<figref idref="DRAWINGS">FIG. 5</figref> illustrates a processing system operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment.

DETAILED DESCRIPTION

The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents.

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a drying system <b>100</b> of a print shop in an exemplary embodiment. While depicted as a separate element from an upstream printer in <figref idref="DRAWINGS">FIG. 1</figref>, drying system <b>100</b> may comprise an integrated component of a printer. After print heads of a printer have marked a web of print media, the wet, marked print media is driven towards drying system <b>100</b>. Drying system <b>100</b> comprises any system, device, or component operable to dry the marking material applied by the upstream printer onto web <b>120</b>. Drying system <b>100</b> has been enhanced to use non-linear power profiles to establish a baseline level of expected power needed to dry web <b>120</b>. These power profiles vary the power based on the speed of web <b>120</b>. The power profiles may further be generated offline and loaded onto drying system <b>100</b> without the need for a feedback sensor or inline process. Furthermore, in one embodiment drying system <b>100</b> can deviate from that baseline level of power in order to account for unexpected variations in ambient humidity, temperature, etc. in order to ensure optimal drying of web <b>120</b>.

In this embodiment, drying system <b>100</b> includes heating element <b>110</b>, reflector <b>130</b>, sensor <b>140</b>, and controller <b>150</b>. Drying system <b>100</b> provides different levels of power to heating element <b>110</b> based on stored power profiles. Each power profile defines a different non-linear relationship between the speed of web <b>120</b> and power to apply to heating element <b>110</b>. Thus, one power profile may be optimized for a certain type of media and/or marking material, while another power profile may be optimized for another type of media. Sensor <b>140</b> is capable of providing feedback indicating whether portions of web <b>120</b> have been sufficiently dried when they exit drying system <b>100</b>. Based upon this feedback, in one embodiment drying system <b>100</b> can deviate the amount of power applied so that it is more or less than the amount suggested by the power profile.

Web <b>120</b> travels through drying system <b>100</b>, and may comprise any suitable media capable of receiving marking material. For example, web <b>120</b> may comprise a web of paper. Depending upon the type of material used for web <b>120</b>, it may take more or less energy to dry marking material onto web <b>120</b>.

Heating element <b>110</b> is operable to generate radiant energy when it is powered. As web <b>120</b> travels through the interior of drying system <b>100</b>, heating element <b>110</b> applies the generated radiant heat (indicated with element <b>112</b>) to web <b>120</b> in order to heat web <b>120</b> and affix marking material onto it. Reflector <b>130</b> enhances the drying process by reflecting radiant heat from heating element <b>110</b> back towards web <b>120</b>.

Controller <b>150</b> regulates the operations of heating element <b>110</b>, and comprises any suitable system, component, or device operable to manage the amount of power directed to heating element <b>110</b> (e.g., by varying an applied power to heating element <b>110</b> as a function of the speed of web <b>120</b>). For example, controller <b>150</b> may be implemented as a processor that implements programs stored in a memory. Controller <b>150</b> is capable of selecting a power profile from memory to use when drying web <b>120</b> (e.g., based on the type of media that web <b>120</b> is made from). Based on the speed of web <b>120</b>, controller <b>150</b> can use the selected power profile to adjust the amount of power applied to heating element <b>110</b>. Controller <b>150</b> is further capable of receiving feedback from sensor <b>140</b>, and deviating from a selected power profile based on this feedback. This allows controller <b>150</b> to account for unexpected deviations in ambient room temperature, humidity, ink viscosity, and other factors.

Sensor <b>140</b> comprises any sensor capable of measuring a characteristic indicative of whether web <b>120</b> is dry as it leaves dryer <b>130</b>. For example, sensor <b>140</b> may comprise a temperature sensor (e.g., a laser temperature sensor) that measures the temperature proximate to a surface of web <b>120</b>. Controller <b>150</b> may then extrapolate the dampness of web <b>120</b> based upon a measured temperature reading. To ensure consistent temperature readings, sensor <b>140</b> may be set up to measure only marked or only unmarked portions of web <b>120</b>. In other embodiments, sensor <b>140</b> may comprise a humidity sensor that measures a moisture content at web <b>120</b>.

Further details of the operation of drying system <b>100</b> will be discussed with regard to <figref idref="DRAWINGS">FIG. 2</figref>. Assume, for this embodiment, that a print shop operator wishes to initiate printing of a print job onto web <b>120</b>. The operator may contact controller <b>150</b> (e.g., via a user interface or remote client), and select the material that web <b>120</b> is made of. The operator may further indicate the type of marking material that will be printed onto web <b>120</b>. Controller <b>150</b> may then select a power profile to use when drying web <b>120</b> based on the operator's input (e.g., based on input indicating the material of web <b>120</b> and/or type of marking material used). In a further embodiment, controller <b>150</b> may select a power profile based upon input from a job ticket, based on a message from a print server, or even based on an analysis of the print data itself for specific metadata or other information.

Next, a printer upstream from drying system <b>100</b> initiates printing onto web <b>120</b>. During the printing process, web <b>120</b> is driven downstream toward drying system <b>100</b>. The damp printed portions of web <b>120</b> are therefore moved from the printer and into drying system <b>100</b>.

<figref idref="DRAWINGS">FIG. 2</figref> is a flowchart illustrating a method <b>200</b> for drying a web of print media in an exemplary embodiment. The steps of method <b>200</b> are described with reference to drying system <b>100</b> of <figref idref="DRAWINGS">FIG. 1</figref>, but those skilled in the art will appreciate that method <b>200</b> may be performed in other systems. The steps of the flowcharts described herein are not all inclusive and may include other steps not shown. The steps described herein may also be performed in an alternative order.

In step <b>202</b>, controller <b>150</b> determines a speed of web <b>120</b> as it travels through drying system <b>100</b>. This action may be performed by querying a networked printing server to retrieve the speed, by reading one or more sensors within the print shop (e.g., at an entrance or exit of drying system <b>100</b>), or by physically measuring the speed of the web. Physically measuring web speed may comprise measuring a rotational velocity of one or more rollers, or using a linear velocity sensor to measure actual web speed.

In step <b>204</b>, controller <b>150</b> applies power to heating element <b>110</b> in order to dry web <b>120</b>. The amount of power is chosen based upon the selected power profile. This power profile may be defined by one or more equations, or may be defined as a series of empirically determined data points stored in memory. The equations and/or points may be used by controller <b>150</b> to determine a relationship between speed for web <b>120</b> and power applied to heating element <b>110</b>. If the power profile is defined as a series of data points, then controller <b>150</b> may perform an interpolation (e.g., linear, quadratic, etc.) between points to determine a power to apply to heating element <b>110</b> at a given speed. Applying power may be performed, for example, by changing the voltage applied to heating element <b>110</b>.

In step <b>206</b>, sensor <b>140</b> optionally measures portions of web <b>120</b> while/after these portions of web <b>120</b> leave drying system <b>100</b>. The measurement is performed to determine whether these portions of web <b>120</b> are still damp. Sensor <b>140</b> may measure the temperature of web <b>120</b> as it exits dryer <b>130</b>, the humidity at web <b>120</b>, etc.

Marked portions of web <b>120</b> can be heated to much higher temperatures than unmarked portions of web <b>120</b>, because their spectral absorption properties will be different. Marked portions of web <b>120</b> will therefore absorb a different amount of radiant heat. Therefore, sensor <b>140</b> can be calibrated to consistently measure either marked or unmarked portions (e.g., margins) of web <b>120</b> so that the measurements do not unexpectedly change.

In one embodiment, controller <b>150</b> analyzes the measurements from sensor <b>140</b> to determine if web <b>120</b> is within appropriate bounds of dryness/dampness when it exits drying system <b>100</b>. If web <b>120</b> is too dry, there may be a risk of fire or discoloration of the printed media. At the same time, if web <b>120</b> is too damp, then marking material (e.g., ink) on web <b>120</b> may smear when web <b>120</b> is driven downstream of drying system <b>100</b>, or is stored at the print shop. Therefore, if web <b>120</b> is over a threshold for dryness or below a threshold for dampness, it may be desirable to adjust the power applied to heating element <b>110</b> to get web <b>120</b> as dry as desired. These thresholds vary based on the power profile, as one type of print material for a web may use more or less power to achieve the same level of dryness than another type of print material for a web.

In step <b>208</b>, controller <b>150</b> optionally deviates the power applied to heating element <b>110</b> away from the power profile to account for web <b>120</b> being too dry or too damp. Steps <b>206</b> and <b>208</b> may be performed iteratively, such that multiple small changes are made to the power applied to heating element <b>110</b> over time. For example, if the web is too dry, controller <b>150</b> may substantially reduce the amount of applied power to eliminate fire risk, and may then slowly increase the applied power over time to reach an optimum level of drying.

Using method <b>200</b>, drying system <b>100</b> can more effectively dry a web of print media. For example, controller <b>150</b> can initially establish a baseline level of expected power needed to dry the web based on the power profile. Furthermore, controller <b>150</b> can in further embodiments deviate from that baseline level of power in order to account for unexpected variations in ambient humidity, temperature, etc., and ensure optimal drying.

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram illustrating various power profiles for dryer systems in an exemplary embodiment. In each of the power profiles, a power applied to a radiant heater is correlated with a linear speed of a web of print media. <figref idref="DRAWINGS">FIG. 3</figref> includes two profiles <b>310</b> and <b>320</b>, which are linear power profiles. Linear profile <b>310</b> is optimized for low-speed printing, while linear profile <b>320</b> is optimized for high-speed printing. For linear profiles, at lower printing speeds (e.g., speed “A”) the web is left damp and underheated. At high speeds however, (e.g., speed “B”) the web is overheated and risks igniting a fire. Non-linear profiles <b>330</b> and <b>340</b> utilize fixed operating points that indicate a desired voltage to apply for a given speed of printing. A controller may then use interpolation (e.g., linear, quadratic, etc.) to estimate between these fixed operating points. The overall function for applied voltage is therefore not a linear one.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating modifications applied to a power profile <b>330</b> for a dryer system in an exemplary embodiment. According to <figref idref="DRAWINGS">FIG. 3</figref>, non-linear profile <b>330</b> has been modified by controller <b>150</b> of <figref idref="DRAWINGS">FIG. 1</figref> to exhibit altered behavior. For example, controller <b>150</b> has modified its use of profile <b>330</b> to include cut-off points <b>410</b> and <b>420</b>. In this example, controller <b>150</b> leaves heating element <b>110</b> powered off when the speed exceeds cutoff <b>420</b> or drops below cutoff <b>410</b>. Powering off heating element <b>110</b> at low speeds ensures that if web <b>120</b> comes to a stop, latent heat from heating element <b>110</b> will not burn web <b>120</b> as it rests within the dryer. Powering off heating element <b>110</b> at high speeds ensures that design thresholds for optimal operation of heating element <b>110</b> are not exceeded.

<figref idref="DRAWINGS">FIG. 4</figref> also shows deviations from power profile <b>330</b>. At location <b>430</b>, a measurement made by sensor <b>140</b> of <figref idref="DRAWINGS">FIG. 1</figref> (indicating that the web is too damp) has caused controller <b>150</b> to increase the amount of voltage applied to a radiant heater in order to make the web more dry, even though the speed of the web is relatively slow. This may be appropriate when the ambient humidity of the print shop is unexpectedly high.

Location <b>440</b> indicates a different printing scenario where printing occurs at a different speed. In this scenario, a measurement made by a sensor (indicating that the web is too hot) has caused controller <b>150</b> to decrease the voltage applied to heating element <b>110</b> in order to make the paper less dry and less likely to catch fire. Controller <b>150</b> then pauses for the system to stabilize (e.g., for ten seconds, a fraction of a second, etc. depending on web speed and/or sensor placement) and takes another measurement from sensor <b>140</b>. Controller <b>150</b> then determines from the sensor input that the web is still too dry, and drops the voltage again. Controller <b>150</b> waits again and takes another reading. This time, controller <b>150</b> determines that the web is too damp, and performs a minor increase in voltage applied to heating element <b>110</b>. This adjusts the voltage to ensure that web <b>120</b> is dry but not dangerously hot (e.g., 400° F.) when it leaves the dryer. This voltage adjustment process may be continuously performed until the print job has completed.

In a further embodiment, controller <b>150</b> may continuously sample the printing speed for a given job, and may dynamically adjust the voltage applied to a radiant heater whenever the printing speed changes during printing of the job. This may be advantageous in situations where a printer slows down the speed of a web in order to account for increased rasterization time for complex segments of print data. This may also be advantageous when manual print quality verification is performed by a print shop operator.

In a further embodiment, controller <b>150</b> may take advantage of the observation that marked portions of a web of print media become much hotter than unmarked portions. In this embodiment, when the dryer initializes, it initializes by receiving unmarked, blank portions of a web. The controller may therefore “pre-heat” the dryer before a print job is initiated. During this pre-heat process, controller <b>150</b> may increase the power applied to heating element <b>110</b> to the point where marked portions of the web would ignite due to the applied radiant heat emanating from heating element <b>110</b> (i.e., regardless of the current operating temperature of the dryer).

This pre-heat power may continue until the print job initiates and printed portions of the web start traveling nearing the dryer. At this point, controller <b>150</b> may drop the amount of power applied to heating element <b>110</b> to keep it from igniting the printed portions of the web as they travel through the dryer. Controller <b>150</b> may determine that printed portions of the web are nearing the dryer based on a known speed of the web and a known distance from the printer to the web. The pre-heat process herein discussed enables the dryer (and downstream web handling components) to rapidly reach a desired operating temperature whenever a new print job is initiated.

In a further embodiment, controller <b>150</b> performs a linear interpolation between voltages defined by the power profile. For example, controller <b>150</b> may detect the printing speed (S_current) by querying the printer, and then select two operating points within the power profile. The first operating point (V₁) is at a speed (S₁) below the printing speed, while the second operating point (V₂) is at a speed (S₂) above the printing speed. Controller <b>150</b> interpolates a voltage to apply by using the following formula: <br /><i>V</i>_current<i>=V</i>₁+(<i>V</i>₁<i>−V</i>₁)*(<i>S</i>_current<i>−S</i>₁)/(<i>S</i>₂<i>−S</i>₁)

Embodiments disclosed herein can take the form of software, hardware, firmware, or various combinations thereof. In one particular embodiment, software is used to direct a processing system of drying system <b>100</b> to perform the various operations disclosed herein. <figref idref="DRAWINGS">FIG. 5</figref> illustrates a processing system <b>500</b> operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment. Processing system <b>500</b> is operable to perform the above operations by executing programmed instructions tangibly embodied on computer readable storage medium <b>512</b>. In this regard, embodiments of the invention can take the form of a computer program accessible via computer-readable medium <b>512</b> providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium <b>512</b> can be anything that can contain or store the program for use by the computer.

Computer readable storage medium <b>512</b> can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium <b>512</b> include a solid state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W), and DVD.

Processing system <b>500</b>, being suitable for storing and/or executing the program code, includes at least one processor <b>502</b> coupled to program and data memory <b>504</b> through a system bus <b>550</b>. Program and data memory <b>504</b> can include local memory employed during actual execution of the program code, bulk storage, and cache memories that provide temporary storage of at least some program code and/or data in order to reduce the number of times the code and/or data are retrieved from bulk storage during execution.

Input/output or I/O devices <b>506</b> (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled either directly or through intervening I/O controllers. Network adapter interfaces <b>508</b> may also be integrated with the system to enable processing system <b>500</b> to become coupled to other data processing systems or storage devices through intervening private or public networks. Modems, cable modems, IBM Channel attachments, SCSI, Fibre Channel, and Ethernet cards are just a few of the currently available types of network or host interface adapters. Presentation device interface <b>510</b> may be integrated with the system to interface to one or more presentation devices, such as printing systems and displays for presentation of presentation data generated by processor <b>502</b>.

Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.